This invention relates to an internal combustion engine and more particularly to variable valve timing and lift arrangement for such engines. It has been recognized that the performance of an internal combustion engine can be improved throughout the entire running range if a variable valve timing and lift arrangement is employed in connection with the engine. By changing the valve opening characteristics during engine running, it is possible to optimize the valve timing and lift for each running condition.
One way this has been done is by providing a first cam and a second cam that rotate together and wherein one of the cams is moved to a retracted position during the rotation so that the other can controls the valve operation during one engine running phase. By shifting the normally disabled cam to an engaged or operative position, it is possible to then change the timing and lift characteristics. However, the types of mechanisms that have been proposed for this purpose are quite complicated and subject to difficulty in operation and transition from one phase to the other.
It, therefore, a principal object to this invention to provide an improved variable valve timing and lift arrangement for an internal combustion engine.
It is further object to this invention to provide a variable valve timing and lift mechanism employing two different cams, each of which is operative to control the valve timing during a specific engine running condition with the running conditions controlled by each cam being different.
It is a further object to this invention to provide an improved variable valve timing mechanism of the type set forth in the preceding paragraph wherein the transition can be made easily and at any time during the engine running characteristics.
It is a further object to this invention to provide an improved variable valve timing mechanism for an internal combustion engine wherein the number of components required operating a plurality of valves is reduced.
One feature of the invention is adapted to be embodied in an internal combustion engine that has a combustion chamber. At least one gas flow passage communicates with the combustion chamber through a valve seat and a poppet valve controls the flow through the valve seat. A camshaft is journalled for rotation about a camshaft axis. A first cam having a first lift characteristic is fixed for rotation with the camshaft. A second cam is associated with the camshaft and has a second lift characteristic different from the first lift characteristic of the first cam. A valve actuator is associated with the first and second cams for transmitting their rotational movements to reciprocation of the poppet valve. A coupling device is provided for selectively permitting relative rotational movement between the camshaft and the second cam so that the first cam controls the entire opening and closing cycle of the poppet valve and for coupling the second cam for rotation with the camshaft about the camshaft axis so that the second cam controls at least a part of the opening and closing operation of the poppet valve.
Another feature of the invention is adapted to be embodied in an internal combustion engine as set forth in the preceding paragraph and wherein a second poppet valve is provided for opening and closing a second valve seat in the combustion chamber and a third cam. The cams are juxtaposed axially on the camshaft and one of the first and second cams have portions for controlling the opening and closing cycles of both of the poppet valves. The other of the first and second cams controls at least a portion of the opening and closing of only one of the poppet valves and the third cam controls at least a portion of the opening and closing cycle of the other of the poppet valves.
FIG. 1 is a cross sectional view taken through one of the intake valves and one of the exhaust valves seats of a single cylinder of the cylinder head portion of an internal combustion engine constructed in accordance with an embodiment of the invention.
FIG. 2 is a view looking in the direction perpendicular to the plane about which FIG. 1 is taken and shows the valves associated with the intake side of two cylinders of the cylinder head.
FIG. 3 is an enlarged cross sectional view taken through the axis of the intake camshaft as shown in FIG. 2 as showing the relationship between one of the low speed cams and the camshaft.
FIG. 4 is a cross sectional view taken along the line 4xe2x80x944 of FIG. 3.
FIG. 5 is a cross sectional view, in part similar to FIG. 3, but shows the relationship between the camshaft and the high speed cams.
FIG. 6 is a cross sectional view taken along the line 6xe2x80x946 of FIG. 5.
FIG. 7 is a cross sectional view, in part similar to that of FIG. 6, but shows another embodiment of the invention.
FIG. 8 is a cross sectional taken along the line 8xe2x80x948 of FIG. 5 and shows the high speed cam in its disengaged non-valve operating position.
FIG. 9 is a cross sectional view, in part similar to FIG. 8, and shows the high speed cam in its engaged, valve operating position.
FIGS. 10 through 16 are cross sectional views taken through one of the intake valves and showing the condition when the intake valve is opened and closed solely under the control of the low speed cam.
FIGS. 17 through 23 are cross sectional views, in part similar to those of FIGS. 10 through 16, and show how the eccentric bearing support for the high speed cam permits it to move in a radial direction so that it will not effect the operation of the valve.
FIGS. 24 through 29 are a sequential series of cross sectional views, in part similar to FIGS. 10 through 16 and show when the high speed cam is controlling the operation of the valve.